1. Field of the Invention
The field of the invention is ionization smoke detectors. More particularly, the field of the invention is ionization smoke detectors utilizing a single ionization source.
2. Description of the Prior Art
Heretofore various configurations for ionization smoke detector chambers utilizing a single radioactive source have been proposed. Examples of such ionization smoke detectors can be found in the following U.S. patents:
______________________________________ U.S. Pat. No. PATENTEE ______________________________________ 3,560,737 Skildum 3,935,465 Beyersdorf 3,935,492 Sasaki et al. 4,012,729 Weaver et al. 4,044,262 Minowa 4,044,263 Ried, Jr., et al. 4,093,886 Blackwell ______________________________________
The detector disclosed in U.S. Pat. No. 3,560,737 utilizes an anode carrying a radioactive source which is surrounded by a cup shaped second electrode which in turn is surrounded by a cup shaped third electrode. Windows are provided in the second electrode for permitting ionization currents between the anode and the third electrode.
In U.S. Pat. No. 4,044,262 there is disclosed a first electrode having a radioactive source mounted on the end thereof, a second cup shaped electrode surrounding said first electrode and having an opening in the center thereof concentric with said first electrode and a third cup shaped electrode positioned about and coaxial with the second electrode.
U.S. Pat. No. 3,935,492 discloses a smoke detector having a first electrode, a metallic screen surrounding said first electrode and forming a second electrode and a larger metallic screen surrounding the smaller screen and having a radioactive source therein which irradiates the space within the larger screen and the space within the smaller screen in which is mounted the first electrode.
In U.S. Pat. Nos. 4,012,729 and 4,093,886 there is illustrated a detector having a cylindrical metallic housing forming one electrode, an electrode mounted on an insulator at one end of the housing and having an ion particle source situated thereon and a ring electrode spaced slightly above and coaxial with the end electrode having the ion particle source. The opening in the center of the ring electrode is coaxial with the radioactive source.
U.S. Pat. No. 4,044,263 discloses a detector including a first button shaped electrode mounted on an insulator within a housing which defines a second electrode. A signal electrode extends axially on the axis of the housing and of the second electrode and is separated from the first electrode by a relatively small distance and has a bent laterally extending portion.
U.S. Pat. No. 3,935,465 discloses a smoke detector with a cup shaped housing that has a depressed center wall and an arrangement of inlet openings into a smoke detection chamber which provides for diffusion of high velocity air currents impinging upon the cup shaped housing. This configuration provides for the entrance of ambient air in a radial direction into the housing.
As will be described in greater detail hereinafter, the ionization smoke detector of the present invention differs from the previously proposed smoke detectors described above by providing for a sensing electrode in a smoke detector chamber which is spaced axially from and laterally to one side of a first electrode mounting a radioactive source. Also, the ionization smoke detector of the present invention provides a second cup shaped electrode which is spaced from the first electrode and which has portions of the peripheral sidewall of the cup shaped second electrode punched in to form inlets which provide for the entrance of ambient air in a circumferential direction into the interior space within the cup shaped second electrode.